(Defacto) standard DC barrel connectors

[Karel]

Is there a (defacto) standard or informal list of DC barrel connectors that tells which size
(inner diameter, outer diameter, length) to use for 5, 12, 24V etc.?
If not, what is most common for 5VDC and for 12VDC?

edit: I just found this: https://en.wikipedia.org/wiki/Coaxial_power_connector?useskin=vector#IEC_60130-10

[Berni]

The great thing about standards is that there is so many to choose from. 

[Jeroen3]

Are the sizes supposed to be coded to voltage?

[Gyro]

Are the sizes supposed to be coded to voltage?

If only! They're not even coded for polarity.

[nctnico]

The ones with a 2.1mm or 2.5mm center pin seem to be most common. Just look at the wall-wart / desktop power supplies you can buy from Digikey, Farnell, etc.

[Berni]

Yep best way to find the common standard is to go on aliexpress and search for a wallwart of the desired voltage then see what connector they most commonly come with.

For 12V they did seam to have standardized on one particular dimension. For 5V there seams to be 2 common standard dimensions. For 18V there is a common dimension (these are laptop chargers). For other voltages it seams to be a wild west mostly.

[ebastler]

I don't think there is any standard or even loose convention, and no correlation between voltage and plug diameter.

I have three laptop computers in front of me here, all a tad before the USB-C era. All three use 19V power supplied via barrel jacks, and they use three different plug diameters. If anything, the plug diameter is correlated with the physical size (thickness) of the laptop.

[PlainName]

The only 'standard' I know of is 2.5mm pin for 5V, 2.1mm for >5V. The idea is that you can't then plug a 12V supply into something expecting 5V. However, although this seems to be common it's not common enough that you won't get caught out sometime.

[Monkeh]

Japan has a standard: https://en.wikipedia.org/wiki/EIAJ_connector

Nobody else takes any notice.

[rdl]

Nearly all the AC adapters I've owned in the last 20 years, 5, 9, or 12 volt, use 2.1mm/5.5mm center positive for the output. I think the few that used 2.5mm center post were higher power devices (>1 amp).

[magic]

Same here, mostly a random mix of 5.5/2.1 and 5.5/2.5, except that the lowest 5.5/2.5 I have seen was 1A exactly.
DC and AC.

Space constrained devices sometimes used smaller connectors with 3~4mm outer diameter.

[nctnico]

Then again, if the OP is looking to design a product it could be worth considering using USB-C and a small chip that negotiates the required supply voltage.

[coppice]

Japan has a standard: https://en.wikipedia.org/wiki/EIAJ_connector

Nobody else takes any notice.

That seems to be the only standard that links the power connectors it defines to their application - i.e. which way around to polarise them, what the voltage is, etc. Its a pity they are not more widely used. Even the Japanese don't use them that widely.

[Siwastaja]

There is no standard, not even de facto. If you want to use a barrel connector in your product, you just write in the manual that only the supplied adapter is allowed and using anything else voids warranty, and then you let users either be careful choosing the right voltage and polarity, or kill your product and (hopefully) learn from that.

Luckily, with USB power everywhere, DC plugs are rarer today and as such, users are less likely to pull any random power supply and try to use it with your product instead of your supplied adapter.

[coppice]

There is no standard, not even de facto.

Get with the program. Two of us just referenced a real standard. There is one. Few people follow it. There are also de facto standards. Find a CCTV camera that doesn't have the same connector with the same polarity and 12V requirement as the rest. If you can it will be a strange outlier, or something specialist with unusual power needs.

[ebastler]

Find a CCTV camera that doesn't have the same connector with the same polarity and 12V requirement as the rest. If you can it will be a strange outlier, or something specialist with unusual power needs.

Unusual choice of example. I would argue that any CCTV camera is a "strange outlier" today, and has been for 10 years or so. Isn't everything TCP/IP based these days?

[coppice]

Find a CCTV camera that doesn't have the same connector with the same polarity and 12V requirement as the rest. If you can it will be a strange outlier, or something specialist with unusual power needs.

Unusual choice of example. I would argue that any CCTV camera is a "strange outlier" today, and has been for 10 years or so. Isn't everything TCP/IP based these days?

Those are CCTV cameras. Many have a PoE power option, but they usually have a 12V barrel connector, too. I think they want to be able to sell as drop in replacements, so they want to be able to reuse existing power wiring.

[tom66]

Find a CCTV camera that doesn't have the same connector with the same polarity and 12V requirement as the rest. If you can it will be a strange outlier, or something specialist with unusual power needs.

Unusual choice of example. I would argue that any CCTV camera is a "strange outlier" today, and has been for 10 years or so. Isn't everything TCP/IP based these days?

It's still pretty common for smaller CCTV systems to use analog HD cameras.  These use a modified "PAL" format to transmit colour analog HD video over a single coax cable.  The one I have does 1440x1080i @ 30Hz with a 25MHz colourburst frequency.  I'm even aware of 4K capable cameras, though their frame rate is quite low: 10-15Hz.  OK for CCTV though.

PoE and IP cameras are common too but a bit more expensive in my experience.

[BrokenYugo]

Then again, if the OP is looking to design a product it could be worth considering using USB-C and a small chip that negotiates the required supply voltage.

This, a USB PD charger is a universal wall wart that does the voltage setting automatically. Adds a lot of idiot proofing when you can't break things by simply plugging the wrong stuff together.

What I do for the 5.5mm barrel jack stuff I have is lots of labels, flag on end, one on brick, one on device if it isn't clearly labeled.

[madires]

As the family's repair shop I see tons of wall warts and power bricks. The most widely used barrel connector is 5.5/2.1, followed by 5.5/2.5 and different smaller ones, rarely larger types. Voltages are all over the place, and the larger connectors are typically used for higher currents. Another thing to note is that many connectors come in two lengths (usually 9 and 14mm).

[SiliconWizard]

Yes to the above, 5.5/2.1 is very common, and yes obviously it could be any voltage. That's even the whole point of these connectors, flexibility.
As madires pointed out, one important thing is to match the length both for the connector and plug. Nothing more unpleasant (both looks, reliability and even susceptibility to ESD) than a male plug that's too long for the receptacle and has a significant part of it exposed when plugged. A properly matched plug should not show any metal part when plugged in.

As to using USB-C instead, your call. May look appealing at first, but it's a whole other rabbit hole in its own right.